Optical comparator



J. Q. ADAMS ET AL 55, 8

OPTICAL COMPARATOR April 18, 1939.

Filed Aug. 20, 1937 Pig. 2.

Inventors: John Q. Adams Frank A. Benford,

OPTKCAL COMPARATOR John Q. Adams and Frank A. Benford, Schenectally, N. Y, assignors to General Electric Company, a corporation of New York Application August 20,

6 Claims.

Our invention relates to a method of and apparatus for obtaining an equally magnified visual comparison of two physical objects. For example, by means of our invention, greatly magnified images of male and female machine parts, such as punches and dies, valve seats, and valves, and other objects may be superimposed on a screen to determine the exactness of their fit, clearance, comparative size, etc.

In carrying our invention into efl'ect, we provide an optical system by means of which the surfaces of the parts to be compared are illuminated and their surface images magnified and simultaneously projected in complementary su perimposed relation ona screen. While the parts are thus set up in the comparator, they may be worked upon and fitted as by grinding. Minute changes in the relative dimensions and shapes of the two parts which are too small to be detected by the unaided eye are thus made easily visible as the fitting operation proceeds. The apparatus greatly facilitates the exact fitting of small parts, the obtaining of a definite uniform clearance between parts, etc.

The features of our invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a bet.- ter understanding of our invention, reference is made in the following description to the accome panying drawing in which Fig. 1 is a front view and Fig. 2 a side view of one embodiment of our invention showing an optical comparator suitable for comparing a punch and its die. Parts oi. the optical system are shown in Figs. 1 and 2. Fig. 3 oillustrates schematically a preferred arrangement of such optical system; Fig. 4 is a reproduction of the superimposed screen images of parts of a punch and die as obtained by our apparatus; and Fig. 5 represents an inferior method of illumination that will be referred to in explaining our invention.

Referring now to the drawing and principally to Figs. 1 and 2, we have shown a'supporting structure for holding the parts to be compared in adjustable relation with respect to the optical system and screen chamber also supported by the structure. The pieces to be compared are represented as a punch plate it and its die plate H, such as are employed in punch press work on sheet metal. In order that the size, spacing, and shape of the openings to be punched shall be accurate and the punch and die used therefor shall have a reasonably long life, it is essential that the punch and die shall conform to exact dimensions and be accurately fitted in relation to each other.

1937, Serial No. 160,112

The punch and die parts, which are to be used together, are thus set up in a manner to obtain enlarged equally magnified images of both in overlapping relation and to allow the parts to be worked upon and fitted and the results of such fitting operations observed on an enlarged scale as the fitting operations proceed. The supporting standard I2 is provided with various adjustable table parts slidable in guideways in order that the parts under observation may be raised, 10 lowered, and moved horizontally as necessary or desirable to bring various portions of the punch and die into proper focus with respect to the optical system and, at the same time, to be rigidly held in any position to which they may be ad- 15 justed. These adjustable table parts are generally similar to those used on metal-working machine tools. ,The table part l3 may be raised and lowered by means of the handwheel I t and screw jack indicated at l5. Table 33 supports a table it which may be moved horizontally to the right and left, as viewed in Fig. 2, by means of the handwheel operated screw indicated at H.

Adjustment of tables l3 and I6 adjusts both oi the parts In and H simultaneously. The die H is held in a support 08 which is individually adjustable in a horizontal direction on table 16 by means of the screw indicated at is. Also, the die H is rotatable on its horizontal axis in support is by means of the adjustment screws indicated at 20. The punch plate I0 is supported in a holder 2| which is adjustable on table it in horizontal directions by means of the screw indicated at 22 but at right angles to the adjustment of holder l8 afforded by screw l9, and the punch plate to may be raised and lowered in its support 2i by means of the screw indicated at 23. It thus is apparent that the punch and die parts may have their horizontal axes exactly aligned and their individual parts properly oriented so as to face each other in the relation in which they are subsequently to be used in a punch press. Also, by the other adjustments mentioned, these parts may be properly focused with respect to the optical system now to be described.

The surfaces to be compared must be properly illuminated since the present systemuses a refiected light principle. A lamp 2t is provided for illuminating the surface of the punch Ill and a lamp 25 is provided for illuminating the surface 50 of the die it In some cases a single light source for both objects may sufilce. Light from the lamp passes through condensing lenses 26 and it, see Fig. 3, to parabolic mirrors 28 and 29, is then reflected to the surfaces to be compared, and 55 ings provided in the central portions of the mirrors 28 and 29. The effective light rays as reflected from the surfaces to be compared are directed toward each other along the same axis and pass through objective lenses 30 and II placed in the central openings in the parabolic mirrors 28 and 23, respectively.

Light rays from one system, for instance the light reflected from the die H, are turned upward at right angles by a half-silvered prism 32, and the light rays from the other system are reflected by the plain mirrors 33 and 3| so as to enter the prism 32 from the bottom and pass straight through and upward joining the same general path as the light rays from the die H. The paths of the light rays from the two systems are thus joined and enter a darkened chamber 35 through a bottom opening 36, pass upward to a plain mirror 31 on the inner side of the top closure wall of the chamber, are reflected at an angle to another plain mirror 38 on the inside of a second wall of the chamber, and are reflected at another angle to a viewing screen 39 on a third inside wall of the enclosure. Hooded eye openings 4|) are provided in the darkened chamber below or near the lower portion of mirror 38 in order that the screen 39 may be observed from a good viewing angle. The mirror system greatly magnifies the images of the punch and die parts which are thus brought into the focusing range of the optical system. These images are equally magnified and the images are exactly superimposed if the punch and die parts are accurately aligned. Clearness of the images on screen 39 is helped by providing reasonably good reflecting surfaces on the parts to be compared and darkening the recessed surfaces of the openings in the die parts with lamp black so as to contrast sharply with the outer reflecting surface surrounding the opening.

In Fig. 3, the system is represented as focused to compare the fit and alignment of upper male punch projection 4| with the female opening 42 in the die plate. The end surfaces of the punch and the flat surface adjacent the opening 42 are usually finely ground and this leaves them in condition to be used as mirrors. The surfaces need not be smooth enough to make a perfect mirror but should be sufficiently good to be used as specular surfaces.

The general nature of the superimposed images as viewed on the screen is indicated in Fig. 4

where the inner circle represents the image of punch part ll and the outer circle the outline image of opening 42 or the surface contours of the punch and die, respectively. The representation clearly indicates a poor alignment of these individual parts, an error in alignment that could not be detected except for the enlargement picture. The multiplication factor of the optical system can be made as great as fifty and still obtain sufficient reflected light for good images; that is, the image as viewed on the screen may be fifty times larger than the original. This means that the light reflected from the relatively small area of the end surface of punch part 4| is spread out over an area fifty times larger in diameter on the screen, assuming no light is lost in transmission, and it is thus important that the surfaces, the images of which are to be thrown on the screen, reflect as much light as possible in the proper direction. We have found that, if the light from the lamp falls upon the metal faces, such as the face of punch 4|, at an angle close to the perpendicular, a considerable amount of light will be reflected directly to the lenses 30 and 3|. Thus, we have found it desirable to employ parabolic mirrors 23 and 23 properly placed directly in front of the objective to direct the light from the lamp to the objective so that it will be reflected back through the central opening in such mirrors. This method of illuminating the surfaces to be reproduced on the screen assumes that such surfaces are mirror or specular surfaces as distinguished from a method of illumination (see Fig. 5) where the light from source 43 strikes the surface 44 at an angle far from the perpendicular and minute scratches and irregularities in the surface are depended upon to reflect a small part of the light in the useful direction.

It is evident that, with the method of Fig. 5, only a small portion of the light from source 43 is reflected in a given direction. In our preferred method of obtaining a high percentage of useful light, that is, light reflected in the proper direction to eventually reach the screen 39, it is not essential that the surface of the punch or die be subjected to any special finishing or polishing operation other than what is usual in the finishing of such parts. It is recognized that, with the ordinary finished surface, minute tool marks and scratches will remain in the surface that will scatter some of the light, and a per cent reflection of the light in the useful direction is not contemplated. However, we have experimented with both methods of illumination and found that, if the surface of the objectives are considered as plain mirrors and are included in the optical system so that the light strikes the same as close to the perpendicular as feasible, the amount of useful light reflected therefrom is such that clear images with large magnification become possible and that, if the method indicated in Fig. 5 be employed, one must be content with relatively smaller and less clear screen images.

That part of the optical system between the backs of mirrors 28 and 29 and screen chamber 35 is preferably enclosed with an opaque material as indicated at 45, Fig. 1. Elements of the optical system such as the mirrors 28 and 29 which may require adjustment from time to time may be so mounted to permit this as is usual in optical systems. In order to give a general idea of the dimensions of the apparatus which we have found feasible for ordinary purposes, the distance D in Fig. 1 may be 24 inches with other dimensions in the same relative proportion.

The system is shown as focused in Fig. 3 for comparing the upper punch and die elements 4| and 42. It will be understood that, by adjustment of the supporting tables l3 and I6 of Fig. 1, other elements of the punch and die plates Ill and II maybe brought into focus with the optical system and compared.

The size and dimensions of the screen chamber 35 largely determine the degree of multiplication of the optical system. The double reflection permits of a large multiplication without resorting to a long chamber. The screen chamber may be used as a camera by providing a photosensitive film 46 to be drawn in front of the screen to obtain permanent records of the images.

In accordance with the provisions of the patent statutes, we have described the principle of operation of our invention together with the apparatus which we now consider to represent the best embodiment thereof, but we desire to have it understood that the apparatus shown is only illusgreases trative and that the invention may be carried out by other means.

What we claim as new and desire to secure by Letters Patent oi the United States, is:

i. an optical comparator comprising a pair of adjustable supports, a pair of parts held by said supports, said parts having exposed light reflecting surfaces having complementary contour edges to be compared, an optical system including means for illuminating exposed surfaces of the parts to be compared, a system of mirrors and prism means for directing reflected light rays from both of such parts along a common axis, a screen upon which such light rays are directed and image magnifying means interposed in the path of the light rays falling upon said screen whereby equally magnified images of the exposed surfaces of the parts to be compared are thrown upon said screen in complementary superimposed relation.

2. Apparatus for comparing the surface contour of a pair of objects, said objects having flat, light reflecting, complementary surfaces, said apparatus comprising means for illuminating such surfaces, an optical system including mirrors and prism means for directing reflected light rays from such surfaces along a common axis, supports for such objects whereby the light reflecting surfaces of the objects may beproperlyfocusedwithrespect to said optical system, a screen upon which such light rays are directed and image magnifying means interposed in the path of such light rays whereby equally magnified outline images of the light reflecting surfaces or such objects may be 1 simultaneously thrown upon said screen in superimposed complementary relation.

3. An optical comparator comprising a pair of holders in which objects to be compared may be secured, a common supporting structure for said holders and provisions for adjusting said holders relative to each other on said supporting struc-= ture such that the objects to be compared, which may be secured in said holders, may have their opposed surfaces brought into spaced apart faceto face alignment, means for directing light rays on the faces of objects secured in said holders; an optical system located between saidholders for receiving light rays reflected from the aligned ex= posed faces of both objects and directing such.

light rays along a common axis, a darkened chamber into which the light rays are projected, said chamber containing a system of mrrors by means of which light ray images of the aligned exposed faces of the parts to be compared are equally magnified and a surface upon which such magnified images are projected in superimposed complementary relation.

An optical comparator comprising a, sup porting structure whereby two objects to be compared may be mounted in spaced apart face to face alignment, light source means for directing ght rays on to the faces of the objects to be com= pared such that the light such at angles close to the perpendicular, objective lenses positioned in front of each of the objects to be compared for collecting light rays reflected from such faces and directing such light rays toward a common point between the supporting structures, a pair of mirrors for turning the light rays from one of the objects to be compared and a partially reflecting prism for turning the light rays from the other object and projecting both systems of light rays in a given direction along a common axis, means for magnifying the light ray images which are thus projected along the common axis and a viewing screen upon which such magnified images are projected in superimposed relation.

- 5. An optical comparator comprising a light ray, optical system, a supporting structure adapted to receive two objects to be compared in spaced face to face alignment in focusing position with respect to such optical system, said optical system comprising light sources for 11- luminating the surface to be compared, parabolic mirror in front of each such surface for directing light rays from the light sources to the faces of the objects to be compared, said parabolic mirrors having openings in their centers in which objective lenses are placed for receiving light rays reflected from such surfaces and directing such light rays toward a common point between the lenses, a partially reflecting prism at such common point for reflecting one system oi. light rays at right angles and along a given ems, a pair of mirrors for turning the other system of light rays so that they pass through said prism and are projected along said given axis, a viewing screen upon which both systems of light rays are projected, which arrangement resulting in producing superimposed images of the objects to be compared on said screen, and means included in said light ray optical and projecting system for greatly magnifying the light ray images thus produced.

6. An optical comparator for comparing two objects such, for example, as a punch and its die, comprising a holder for securing a punch, a second holder for securing a die, a common supporting structure for said holders having facilities for bringing the punch and die secured in said holders into spaced operative alignment, 2. light ray optical system for producing by reflection a magnified image of the face of the punch, a second light ray optical system for producing by reflection an equally magnified image of the face oi the die, a common screen upon which both of such images are projected, said light ray optical systems being so correlated that when the faces of the punch and die are in operative alignment and the faces oi the punch and die are of the same size and shape their magnified es as produced on the screen are in superimposed complementary relation.

some QAD. as a.

GATE OF CORRECTION Patent No". 2,155,3 8. p 8, -959v JOHN Q. ADAMS, ET AL.

It is hereby certified that ermrappears in the "printed epeeii.;'iear.t5.on of the above numbered patent requiring correction as follows: 5', fizeet column, line 1 1 c1aim5, for the word "opposed" reed exposed; line 11 .6, claim, after "holders" strike cut the semicolon and insert insteadmcmmm; entshould be read with this eeri-eation there and that the said Letters PM the record of the case the Patent offieefi,

in that the same may conform 1m Signed and sealed this 50th day of May, A.D. 1959,

Henry Van Arsdale (Seal) Aeting Cc'mnnimsimwr m? Petemazism 

